On December 17, Bitfinex began requiring an invitation code from anyone attempting to sign up for a new account. However, they did not provide a method for existing users to generate these invitation codes. Then, on December 21, they announced that new users would not be accepted until January 18, 2018.
As soon as Bitfinex creates a way for me to invite new users, I will offer those invitations here.
In the meantime, I can recommend an alternative exchange, KuCoin. KuCoin offers most of the same cryptocurrency exchange options and currencies. The transaction fee there is usually slightly cheaper as well (a flat rate of 0.1% instead of Bitfinex's variable 0.08%-0.2%).
The only exception is IOTA, which KuCoin unfortunately doesn't offer. If you want to buy IOTA, I recommend signing up for CoinSpot.
If you don't mind, I would be grateful if you would sign up for KuCoin or CoinSpot using the links above, which are my referral links.